Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $134.46   9.583%   $147.3453   $147.35   $147.35   $147.30  
  Purchase #2 $205.68   13.516%   $233.4797   $233.48   $233.50   $233.50  
  Purchase #3 $108.79   7.468%   $116.9144   $116.91   $116.90   $116.90  
  Purchase #4 $247.95   5.654%   $261.9691   $261.97   $261.95   $262.00  
  Purchase #5 $9.44   12.812%   $10.6495   $10.65   $10.65   $10.60  
  Purchase #6 $211.63   7.116%   $226.6896   $226.69   $226.70   $226.70  
  Purchase #7 $25.53   5.609%   $26.962   $26.96   $26.95   $27.00  
  7 purchase totals = $943.48       $1,024.0096   $1,024.01   $1,024.00   $1,024.00